1. Field of the Invention
The present invention relates to a semiconductor device with a Schottky junction utilizing aluminum, and adapted for use in an integrated semiconductor circuit device.
2. Related Background Art
In the preparation of a conventional semiconductor device with a Schottky junction, such as a Schottky barrier diode, the aluminum film constituting a Schottky barrier with a semiconductor has been formed by sputtering or evaporation.
However such a conventional method has been associated with a first drawback that Al and Si constituting the Schottky barrier diode react by mutual diffusion in a thermal treatment of 400.degree.-500.degree. C. for forming an ohmic contact after the Al film formation. Also a second drawback lies in a fact that the breakdown voltage of such a diode is lower than that of a PN junction diode.
In the following an additional explanation will be given on the conventional semiconductor device having a Schottky junction.
A so-called PNM type semiconductor device, which a modification of lateral PNP semiconductor device, is so designed to concentrate the current in a Schottky junction formed in a portion corresponding to the collector of the lateral PNP device, thereby realizing a function equivalent to that in the ordinary PNP device. FIGS. 1 and 2 are band charts showing the function states of a PNM device, while FIGS. 3 and 4 are band charts showing the function states of a PNP device, wherein shown are an emitter 201, 210; a base 202, 211; a collector 203, 212; and a depletion layer 204, 213 between the collector and the base. The movement of the positive holes, functioning as the principal carriers, is the same in both devices. FIG. 5 illustrates a conventional PNM semiconductor device, wherein shown are semiconductor substrate 101 for example of p-type; an n.sup.+ buried layer 102 constituting the collector; an n-epitaxial layer 103 constituting the actual device; an isolation area 104; a diffused emitter area 105; emitter and base electrodes 107; Schottky electrodes 118 composed for example of aluminum for constituting Schottky junctions with the epitaxial layer 103; an insulation layer 106 composed for example of SiO.sub.2 for insulating the emitter, base electrodes 107 and the metal layers 118 from the semiconductor surface; and a diffusion layer 109 for electrical connection with the base electrode 107.
Also FIG. 6 shows a conventional structure in which a Schottky junction is utilized in the drain portion, wherein shown are an n-type semiconductor substrate 111; a diffusion layer 112 constituting a source area; an isolation oxide film 113 formed for example by LOCOS (local oxidation of silicon); an insulation layer 114 composed, for example, of phosphor glass; a Schottky electrode 115 composed, for example, of Al; a gate oxide film 116; a gate electrode 117; and a source electrode 108.
The conventional PNM semiconductor device shown in FIG. 5 has been associated with a drawback of an extremely low current collecting efficiency because of a planar structure of the Schottky junction. As shown in FIG. 7, the depletion layer 119 generated at the Schottky junction (collector) is concentrated in the surface area of the device and is therefore unable to efficiently collect the carriers diffusing from the emitter, so that the carriers leak to the device isolation area, leading to a lowered current gain. It is also necessary to effect control on the silicon substrate so as to realize satisfactory interface characteristics.
Also as shown in FIG. 8 which is a magnified view of FIG. 7, the depletion layer 119 generates a protruding portion 119a extending along the surface of the device, thus forming a generation/recombination (G-R) area and hindering the improvement in the device characteristics. It is also conceived, in order to prevent such drawback, to form a highly doped layer 120 in a position corresponding to said protruding portion 119a as shown in FIG. 9, but a significant improvement in the characteristics cannot be expected with such structure since the area of the depletion layer 119 is inevitably limited.